This invention has relation to the invention described in U.S. Pat. No. 5,586,484, "Expresso Coffee Maker", which has commnon inventorship and ownership herewith. The patent describes a two-container coffee maker in which coffee grounds are placed within a subassembly called the coffee basket assembly. The coffee basket assembly comprises a hollow cylinder piece and a piston. During the brewing cycle, the steam generated in the lower container of the maker causes the piston to move upwardly, compressing the grounds between the piston and a perforated plate at the bottom of the upper container. Superheated water and steam from the lower heating container are forced through the coffee grounds. The patented coffee maker subjects the grounds to a unique combination of temperature and compression.
The coffee maker described in the patent is quite useful in extracting essences from the coffee grounds in a quick and efficient manner, producing espresso and other varieties of coffee beverage with outstanding flavor. While effective, the construction of the older invention involved certain high cost elements. For example, the piston top had a plurality of small diameter holes. The hole size and number were chosen to both provide the desired differential pressure across the piston--and resultant compression of the grounds--and to distribute the water and steam through the coffee grounds. Furthermore, continuing research has been conducted to otherwise improve the maker.